1. Field of the Invention
The present invention relates to a switching device for switching on and off by operation of an operation knob which swings, and more particularly to a waterproof-type switching device which is capable of preventing water from entering into its case.
2. Description of Related Art
A switching device used in a vehicle window open/close system (power window system) is provided on an arm rest of a door, a console at the center, or other positions of an automobile. This type of switching device has a switch, a circuit board and other components accommodated inside a case, and a cylinder which is disposed on the upper surface of the case and opens to above and below to communicate with the inside of the case, as disclosed in JP-A-8-180755 and JP-A-5-314864 (Patent References 1 and 2). An operation knob is attached to the cylinder in such a position as to cover the upper opening of the cylinder and in such a manner as to swing on the cylinder in the front-to-rear direction. An operation bar which is connected with the operation knob penetrates through the opening of the cylinder and extends toward the inside of the case so as to transmit the movement of the operation knob to the switch. When the operation knob is operated, its swinging motion in the front-to-rear direction is transmitted through the operation bar to the switch so that the switch is turned on or off in accordance with the swinging motion of the operation knob.
In a typical switching device of this type, a cover for covering the upper surface of the case is attached. The operation knob is exposed through an opening of the cover such that the operation knob can be operated therethrough. Thus, when some raindrops fall on the cover in case of raining or for other reasons, the raindrops scarcely enter into the case of the switching device. However, when a large volume of beverage or the like (hereinafter referred to as “water”) is spilt over the cover, the water enters through the clearance between the opening of the cover and the operation knob and flows downward to the upper surface of the case, reaching the cylinder or other components. The water having reached the cylinder rises through the clearance between the operation knob and the cylinder by the force of flow, and enters through the opening of the cylinder into the case. The water having entered the case may cause corrosion and short-circuit of the switch and circuit board.
Japanese Patent No. 3111221 (Patent Reference 3) discloses a method for preventing entrance of water as in the above case. According to this method, water catching grooves are formed on the upper surface of the case before and after a cylinder. The bottoms of the grooves are inclined toward the front of the case, and/or are mountain-shaped having a watershed at the center. Drain ports penetrating through the deepest portions of the water catching grooves are formed on the front surface and the sides of the case. Nothing is described about prevention of water entrance in Patent References 1 and 2.
According to the method of Patent Reference 3, water having entered through the clearance between a cover (finisher according to the description of Patent Reference 3) and the operation knob toward the upper surface of the case is introduced into the water catching grooves to be captured therein. The water is then guided along the inclined groove bottoms toward the deepest portions at the front, and is discharged through the drain ports which are disposed on the sides of the case and are relatively smaller in size than the width and depth of the water catching grooves. Thus, when the amount of water is large, the water having flowed into the water catching grooves cannot be sufficiently discharged through the drain ports. As a result, water overflows the water catching grooves and goes toward the cylinder. The water having reached the cylinder rises through the clearance between the operation knob and the cylinder and enters into the case in some cases.